Linear position sensor having coaxial or parallel primary and secondary windings

ABSTRACT

A position sensing device including two spaced conductive coils constituting a primary and secondary winding of a transformer. A coupling member is mounted to a moveable object such as an automobile steering mechanism and moves relative the primary and secondary windings. This movement adjusts or alters the transformer coupling between the primary and the secondary and produces a variable output signal which can be correlated through use of appropriate circuitry to the position of the moveable member. Two alternate designs are disclosed. In a first design, the transformer primary and secondary are disposed side-by-side and the coupling member slips over the primary and secondary for relative linear movement. In a second design, the primary and secondary are disposed one within the other and the coupling member fits within a gap between the primary and secondary. A control system for multiple position sensors includes circuitry for activating multiple sensors as well as monitoring return signals from multiple signals. Such a control system can interface other computers within the vehicle such as body control and engine control computers.

CROSS REFERENCE TO RELATED PATENTS

The present patent application is a continuation-in-part of patentapplication Ser. No. 07/427,641 filed Oct. 26, 1989 now U.S. Pat. No.5,036,275, application Ser. No. 07/296,183, filed Jan. 11, 1989,entitled "Linear Position Sensor," to Munch et al.

FIELD OF THE INVENTION

The present invention concerns a sensor that provides a signal thatvaries with motion (translation or rotation) according to a functionsuch as a voltage transfer function.

BACKGROUND ART

Prior art position sensors are known which make use of a variabletransformer. In simple transformer parlance an M turn primary coil withcurrent "I" passing through the M turns induces a flux in thetransformer secondary given by:

    F1=M*I/R                                                   (1)

where F1 is the magnetic flux (flux) and R is the reluctance of themagnetic path linking the primary to the secondary. When the magneticpermeability of a yoke linking the primary to the transformer secondaryis sufficiently high virtually all of the flux induced by the primarywill be confined in the yoke and result in the flux being approximatelyconstant throughout the transformer (i.e. magnetic circuit of thetransformer). This allows most of the flux produced in the primary (someleakage of flux from the yoke is inevitable) to also link the secondary.Often a small air gap is used to provide the bulk of the reluctance inthe reluctance path (magnetic circuit) and thereby minimize effects dueto variations of permeability in the yoke due to material or temperaturechanges. The flux "F1" induced by the primary will then induce an emf inthe secondary given by: ##EQU1## where "f" is a factor representing thefraction of the flux "F1" produced in the primary that passes throughthe secondary and "N" is the number of turns of the secondary. Thefactor "f" is generally dependent on the geometry and permeabilities ofthe various elements in the reluctance paths linking the primary andsecondary coils. In an ideal transformer f=1. Not mentioned but relevantare hysteresis effects that can effect f & R and core and wire lossesthat can effect the overall power efficiency of the transformers.Variations in geometry and materials to minimize hysteresis effects,inefficiencies, size, and weight are the basis for a broad range oftransformer applications.

The key factors to note in the "fixed" transformer design are:

a) The designs are optimized to minimize the flux loss "f" between theprimary and secondary.

b) In normal operation the reluctance of the flux paths (magneticcircuit) associated with the transformer remain constant.

c) The number of turns on the primary "M" and secondary "N" remainconstant.

Variable Transformers (variable secondary)

As shown in the preceding expression for the induced emf in a secondarycoil in a transformer (V_(sec)) the induced voltage is directlyproportional to the number of turns of secondary (N) linked by the fluxproduced by the primary coil. A common method of varying a signal withrespect to motion is to build a transformer that has a mechanicaltracking element which changes the effective number of turns of thesecondary linked by the flux generated in the primary.

In accordance with one known technique the secondary coil acts as atracking element and passes over the primary. In this example (providedthat the current remains constant in the primary) the value of thenumber of turns of secondary linked by the flux from the coil changeslinearly with changes in the position of the secondary.

A second type of variable transformer uses a wiper that electricallytaps the secondary at the position of the wiper contact. This results inV_(sec) depending only on the number of turns between the upper end ofthe secondary and the point of contact of the wiper. As long as therange of motion of the wiper is constrained to stay within the length ofthe secondary the effective number of turns "N" of secondarycontributing to Vsec is given by:

    N'=n*x'                                                    (3)

where n is the turn density of the secondary and x' is the distancebetween the point of contact of the wiper and the upper end of thesecondary.

Disadvantages of these two types of variable transformer are thenecessity of having an electrical lead connected to the tracking part,wearing of the contact region between secondary and wiper (resulting inbroken contact and/or interwinding shorting of the secondary), and thesize and weight penalties associated with using a yoke to control theflux distribution (i.e. keep flux constant throughout the transformer).

In all the variable secondary designs accuracy can be effected bytemperature effects on the reluctance of the transformer anddifficulties in controlling effects near gaps, ends of windings and/orcores. Further corrective steps include adding compensating coils to thetransformer and signal conditioning. In general the goal in thesedesigns is to achieve a smoothly varying and repeatable V_(sec) (x')which can then be modified in follow-on electronics to achieve thedesired Vsignal(x)'s.

Variable Transformer (variable reluctance)

In transformers of the variable reluctance class a tracking elementchanges the reluctance (R) and/or coupling efficiency (f) of thetransformer as it moves. From the transformer equation (2) givenearlier, it is clear that variations in "f" and/or "R" will directlyeffect the magnitude of V_(sec).

A prior art design is known where a "gap controller," acting as atracker, is moved in and out to change the effective size of the gap. Asstated earlier, in general, the bulk of the reluctance in a transformeris kept across the gap of the transformer. As a result large variationsin gap size can be expected to introduce large variations in overalltransformer reluctance. Some variation in the flux leakage factor "f"can also be expected although in general "f" will be effected far lessthan reluctance. Applying simple magnetic circuit analysis thereluctances of the yoke, cores and gap can be expected to add in seriesresulting in:

    R.sub.t =R.sub.y +R.sub.cp +R.sub.cs +R.sub.g              ( 4)

where R_(t), R_(y), R_(cp), R_(cs), and R_(g) are the reluctances of thetransformer, yoke, primary core, secondary core, and gap, respectively.The transformer equation discussed earlier becomes:

    V.sub.sec =-f*N*M/R.sub.t *(dI/dt)                         (5)

while the action of the "gap controller" results in:

    R.sub.g →R.sub.g (x)==>R.sub.t →R.sub.t (x), (6)

and to a lesser extent

    f→f+@(x) where |@(x)|<<|f|.

This yields:

    V.sub.sec (x)=-f(x)*N*M/R.sub.t (x)*(dI/dt).               (7)

In designs of this type much effort is spent in designing the contoursof the pole pieces and the "gap controller." Fringe fields in the gapcan vary rapidly with changes in gap size and shape. This results in alarge dependence on the contours of components in the gap. In generalthe goal is to achieve a smoothly varying and repeatable V_(sec) (x)that may be modified in follow-on electronics to yield the desiredV_(signal) (x). In some cases it is possible to optimize the contours ofthe pole pieces and "gap controller" to the point where V_(sec) (x)gives the desired V_(signal) (x) directly.

Disadvantages are the sensitivity of the design to gap variations.Fields in small gaps can change rapidly with small changes in gap sizeor geometry. This can impose a severe tolerance constraint which makesthe design extremely sensitive to motion of the gap controllerperpendicular to that of the desired sense motion "x". This iscomplicated by the fact that a "gap controller" will be stronglyattracted to the pole pieces in the gap. Eliminating motionperpendicular to "x" then involves a mounting system that is secureenough to withstand the tractive forces between "gap controller" andpole pieces in the gap in addition to any shock forces present due tovibration or stress on the system.

A clear advantage over the "variable secondary" designs results,however, from not having any electrical leads to the tracking component(gap controller) which can fatigue or work loose.

A slightly different use of a "gap controller" acts to increase ordecrease the reluctance of a shunt path which acts analogously to ashort in an electric circuit. As the reluctance of the "shunt gap" isdecreased below that of the "secondary gap" the flux induced by theprimary will preferentially follow the shunt path as opposed to thesecondary path. In this case the flux leakage parameter "f" is stronglyeffected as the "shunt" path is essentially a form of leakage path. Thereluctance of the secondary path "R_(s) " can also be expected to beeffected but far less strongly than is "f" which is the opposite of theeffect seen in the "variable reluctance" transformer.

As in the "variable reluctance" transformer much effort is spent inoptimization of the contours and materials of the pole pieces and gapcontroller. The disadvantages are dominated by tight tolerancerequirements of the components in the controlled gap and are the same asthose discussed for the "variable reluctance" transformer. In both ofthese types of transformer the contoured pole and controller piecescombined with tight tolerance requirements often imply high cost.

Linear Variable Differential Transformers (LVDT)

In transformers of this kind the output is differential and representsthe signal balance between two secondaries acted on by a single primary.LVDT's are extremely popular. Applications include acoustic, motion, andseismic sensing. A high profile application is seismic sensing for oilexploration.

The LVDT transformer has a core which moves and acts as a trackingelement. The two secondaries are coupled by the primary. The relativeorientation of primary and secondaries remains fixed at all times. Asthe core moves the region of the primary covering the core moves withit. Except for fringe effects near the ends of the core only the regionof the primary covering the core will have any appreciable flux. In thecentral region of the core (in from the ends) the flux induced by theprimary is essentially constant so that the relative balance of fluxlinking the two secondaries (save for end effects) is directlyproportional to the number of turns of each of the two secondaries thatcover the region of the primary filled by the core. As long as the coreis constrained to move so that the two ends of the core are keptentirely within the secondaries and within the primary the fringeeffects from the core ends can be expected to cancel and can be largelyneglected. The behavior of this device can be characterized as follows.The flux in the central region of the core will be given approximatelyby:

    F1=-M/R*(dI/dt)                                            (8)

where M is the number of turns on the primary and R is an effectivereluctance path seen near the central region of the core. The fluxvariation near the ends is in general difficult to characterize and willsimply be represented as:

    F.sub.a =f(I,x') and

    F.sub.b =f(I,x')                                           (9)

where x' is the absolute value of the distance from the center of thecore and f(I,x') represents the flux variation near the ends of thecores. The induced emf in the secondaries is then given by:

    V.sub.seca (x)=V.sub.a -[-f*M*N*x/R*(dI/dt)] and

    V.sub.secb (x)=V.sub.b +[-f*M*N*x/R*(dI/dt)].              (10)

where n is the turn density in the secondaries, x is the position of areference point on the core (but in from the ends of the core) relativeto the boundary between the two secondaries, V_(a) and V_(b) are thevalues of V_(seca) (0) and V_(secb) (0) respectively. V_(a) and V_(b)each contain equal contributions from the integral of f(I,x') over theregion of the core end that is in each secondary. The differentialsignal then becomes: ##EQU2##

It is important to note that V_(a) and V_(b) are constants with respectto x which results in V_(diff) being linear in x.

Accuracies of <100 nm are possible along with very high degrees oflinearity. These factors combined with no electrical leads to thetracking element and the inherent temperature compensation and noiserejection of a differential output account for much of the popularity ofthese sensors.

Disadvantages include the comparatively limited travel of the core withrespect to overall device size (due to the need to keep the ends of thecore away from the boundary region between the secondaries) and a needfor phase detection to determine the sign of "x". Additionally, thesedevices are optimized for accuracy and tend to be expensive (>$100) interms of automotive applications where sensor accuracies and targetprices are generally lower (Accuracies greater than 100 nm & costs ofless than $10).

In certain sensing applications, position and rotation sensors (amongothers) often need to remove or withstand power supply noise, develop atemperature independent voltage reference or directly compensate fortemperature variations. Often in a given system, such as an automobile,the various sensors redundantly develop their own power regulation andtemperature independent voltage reference. Additionally, multiplesensors of a given design can be placed in a given system, i.e.suspension systems have four height sensors. Typically, such sensors areredudantly equipped with identical electronics, i.e. each has its ownexcitation instead of a single shared excitation.

DISCLOSURE OF THE INVENTION

The present invention concerns a position sensing method and apparatusthat is accurate, yet relatively inexpensive to build and has a varietyof applications and configurations suitable for monitoring the position,velocity, or acceleration of a moveable member.

Position sensing apparatus constructed in accordance with one embodimentof the invention includes an elongated field producing member having aninput for energizing the field producing member to produce anelectromagnetic field in the vicinity of the field producing member. Anelongated field responsive member is fixed with respect to the fieldproducing member and oriented in a generally parallel orientation to thefield producing member along the length of the field producing member.The elongated field responsive member has an output for providing anoutput signal in response to an electromagnetic field produced by thefield producing member.

A coupler connected to the moveable member whose movement is to bemonitored moves with the moveable member relative to the field producingand field responsive members. The coupler alters the response of thefield responsive member as the moveable member moves and thereby changesthe signal at the output of the field responsive member.

An exciter circuit is coupled to the input of the field producing memberfor energizing the field producing member and a circuit is coupled tothe output from the field responsive member to correlate changes in theoutput signal with movement of the moveable member.

In accordance with a preferred embodiment of the invention, theelongated field producing and field responsive members are eachconstructed from multiple turn, current carrying conductors wound aroundcenter axes that extend linearly in the same direction. When energized,current passes along the multiple turn current carrying coil of thefield producing member to induce a current in the multiple turn coil ofthe field responsive member. The preferred design allows high accuracyalong a long linear tracking range (note: a curved tracking path is alsopossible) with no electrical contacts between the coupler and otherelements of the system. This design results in a simple geometry andrelatively simple exciter and monitoring circuits for correlatingchanges in output signal from the field responsive member with movementof the moveable member.

In one embodiment, the field producing member has a coil turn density ofN_(p) (x) (x is a coordinate in the direction of movement of themoveable member and when the member moves along a linear pathcorresponds to one coordinate of an orthogonal coordinate system)wrapped on a magnetically permeable core. The permeability of the coremay or may not be manipulated to vary according to a desired "P_(p) (x)"vs "x" relationship where P_(p) (x) is the permeability along the core.Choice of N_(p) (x) and core material(s) will vary with desired outputsignal transfer characteristic V_(out) (x) and temperature responserequirements. The function of the field producing member is the same asthat of the primary in a transformer device, i.e., to produce magneticflux.

A fixed position field responsive member has a turn density of N_(s) (x)wrapped on a magnetically permeable core. The permeability of the core(through material choices) may be manipulated to vary according to adesired "P_(s) (x)" vs "x" relationship where P_(s) (x) is thepermeability along the core.

In a presently preferred embodiment of the invention, the turn densitiesN_(p) (x) and N_(s) (x) are identical as are P_(p) (x) and P_(s) (x),resulting in identical field producing and field responsive members forease of manufacturing.

The field responsive member is placed parallel and immediately next tothe field producing member. In one embodiment of the invention the fieldproducing and field responsive members are located one within the otherand in a second embodiment they extend side by side. Choice of N_(s) (x)and core material will vary with desired transfer characteristic V_(out)(x) and temperature responsive requirements. In the presentconfiguration where N_(p) (x)=N_(s) (x), a linear "V_(out) (x)" vs "x"relationship is achieved. In fact a broad range of linear and nonlinearrelationships are possible by merely adjusting N_(s) (x) as well asN_(p) (x) without changing the device geometry.

A preferred coupling member is formed from a shorted tracking "coil"placed over the side by side field producing/field responsive membersand interposed between the gap between those members in the alternateembodiment. The coupling member moves relative to the field producingand field responsive members and has no electrical connections exteriorto itself. The choice of N_(c) (x) (coupler coil winding density) willvary with desired transfer characteristic (V_(out) (x)) and temperatureresponse requirements. In one configuration N_(c) (x)=1/D where D is thelength of the coupler. This turn density is achieved by using a metaltube as opposed to a wound coil. The metal tube (aluminum in the currentpreferred configuration) offers ease of fabrication advantages over amulti-turn coil without unacceptable losses in device performance. (Notethat the tube acting as a single turn coil or on which a coil is woundmay or may not be magnetically permeable with a "P(x)" vs "x"relationship depending on the desired system response).

The coupler coil responds to the integral of the flux passing throughits length and parallel to its axis through an induced emf on thecoupler coil directly proportional to the integral of that flux, i.e.,

    |EMFcoupler|=Ac*w*|Integral[flux(x)*N.sub.c (x)*dx]|                                         (12)

where w is the angular frequency in radians/second (for sinusoidalexcitation of the primary), x is in the direction of the axis of thecoupler, Ac is a constant and the integral is performed throughout thelength of the coupler. The induced emf then results in current in thecoupler coil which in turn induces magnetic flux in the field producingand field responsive members that is proportional to that current. Thisinduced flux from the coupler results in emf's on both the fieldproducing and field responsive members. On the field producing memberthe emf from the coupler is seen as additional load while on the fieldresponsive member the induced emf is seen as V_(sec) (x).

In an alternate disclosed embodiment of the invention, a sensorsimultaneously monitors position and velocity. This is accomplishedwithout the use of costly differentiating or integrating circuitry.

Different embodiments of the invention are described for a vehicle ridecontrol system that must operate in the harsh environment of theunderside of a vehicle chassis. This use of the invention includes oneconfiguration where one portion of a position sensor probe includesprimary and secondary winding that are parallel and spaced apart. Acoupling member is positioned around both coils, such that the signaldeveloped in the secondary coil increases as the coupling memberoverlies more of the primary and secondary windings. In anotherembodiment of the use of the invention, the primary and secondarywindings are positioned one within the other and separated apart by acavity or gap. The coupling member is positioned between the windings inthe gap such that the presence of the coupling adjustment meansdecreases the transformer coupling between the windings, which causesthe signal developed across the secondary winding to decrease as thecoupling member extends further into the gap between the windings.

The present sensor is commonly utilized in multiplicities of two ormore. In an alternate disclosed embodiment of the invention, electronicsare shared between multiplicities of the sensor. This sharing eliminatesredundancy to minimize component counts for greater reliability andlower cost. This sensor can be combined with certain other sensor typessuch as accelerometers (that can share the same point of measurement) ina common package to minimize electronic, harness, installation andpackaging redundancies. Such a combined package has significant cost andreliability advantages over separate instances of each component.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a non-contact position sensor coupled to avehicle shock absorber;

FIG. 2 is an enlarged sectional view of the position sensor as seen fromthe plane defined by the line 2--2 in FIG. 1;

FIG. 3 is a plan view of a winding assembly that forms a part of theposition sensor;

FIG. 4 is a partially sectioned, exploded side view of the windingassembly;

FIG. 5 is an enlarged sectional view of a distal end of alternatewinding assembly;

FIG. 6 is a section view as seen from the plane 6--6 of FIG. 5;

FIG. 7 is a perspective view of a carrier that supports terminals forrouting signals to and from the winding assembly of FIG. 3;

FIG. 8 is an exploded, partially sectional view of a housing thatsupports the winding assembly;

FIG. 9 is a graphic diagram of the voltage transfer ratio as it relatesto the relative position of portions of a sensor probe according to theembodiment in FIG. 1;

FIG. 10 is an electrical circuit diagram in block form of the electricalcontrol circuit of the invention;

FIG. 11 is an electrical circuit diagram in schematic form of thecontrol circuit in FIG. 10;

FIG. 12 is a diagram illustrating the equivalent circuit for a positionsensor according to the embodiment in FIGS. 1-11;

FIG. 13 is a schematic depiction of a winding assembly and couplingmember that extends only a short distance along the winding assembly;

FIG. 14 is a schematic depiction of an arcuate winding assembly andcoupling member that moves along an arcuate path;

FIGS. 15A--15C depict alternate cross sectional configurations for thewinding assembly and the coupling member;

FIG. 16 is a sectional side view of a second embodiment of theinvention;

FIG. 17 is an enlarged sectional view of a short segment of the FIG. 16embodiment;

FIG. 18 is a sectional view taken along the lines 18--18 in FIG. 17;

FIG. 19 is an electrical circuit diagram partially in block form andpartially in schematic form of the control module of the embodimentillustrated in FIGS. 16-18;

FIG. 20 is a diagram illustrating the equivalent circuit for a sensorprobe according to the embodiment in FIGS. 16-18;

FIGS. 21 and 22 are plots of induced emf vs. coupling member positionwhere variable turn densities are used in the primary and secondary coilwindings;

FIG. 23 is a plot showing a comparison between predicted theoreticaloutput voltages from a position sensor with observed output voltages;

FIG. 24 is a perspective view of a transformer winding formed from awire wrapped around a magnetically permeable core and having acontrolled turn density (windings/length) along the length of the core;

FIG. 25 is a section view as seen from the plane defined by the line25--25 in FIG. 24;

FIG. 26 is a side elevation view of a transformer winding formed from aconductive pattern that is etched or deposited in a controlled patternaround a magnetically permeable core;

FIG. 27 is a section view seen from the plane defined by the line 27--27in FIG. 26;

FIG. 28 is a perspective view showing an alternate embodiment of acoupling member for adjusting transformer coupling between a primary andsecondary winding;

FIG. 29 is a side elevation view of the FIG. 28 position sensor;

FIG. 30 is a schematic depiction of an additional alternate positionsensor;

FIG. 31 is an end view of the FIG. 30 position sensor;

FIG. 32 is a perspective view of a coupling member having a controlledcross section along its extent for adjusting the coupling between twospaced transformer windings;

FIG. 33 is a perspective view of a movement sensor showing elongatedprimary and secondary windings and a coupling tube positioned over thesecondary winding;

FIG. 34 is a partially sectioned view of the FIG. 33 movement sensor;

FIG. 35 is a view as seen from the plane 35--35 in FIG. 34;

FIG. 36 is a perspective view of a movement sensor wherein a primary andsecondary winding are relatively moveable with respect to each other;

FIG. 37 is a partially sectioned side elevation view of the FIG. 36sensor;

FIG. 38 is a partially sectioned end elevation view of the FIG. 36sensor;

FIG. 39 is a perspective view of a movement sensor where a primary andsecondary winding are stationary with respect to each other and amoveable winding core moves in and out of one of the windings;

FIG. 40 is a partially sectioned side elevation view of the FIG. 39sensor;

FIG. 41 is a partially sectioned end elevation view of the FIG. 39sensor;

FIG. 42 is a side elevation view of the position sensor of FIG. 1showing a location of an accelerometer;

FIG. 43 is a plan view of the FIG. 42 sensor;

FIG. 44 is a schematic of an alternate circuit for activating andmonitoring outputs from the sensor;

FIGS. 45-48 are graphs showing winding density controls to enablevelocity sensing using the disclosed sensor;

FIGS. 49 and 50 illustrate alternate mechanisms for adjusting themagnetic permeability of a core for supporting primary or secondarywindings;

FIG. 51 is a perspective view of a movement sensor having primary andsecondary windings fixed to a flat support;

FIG. 52 is a plan view of the FIG. 51 sensor; and

FIG. 53 is an end elevation view of the FIG. 51 sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, and the illustrative embodiments depictedtherein, a non-contact position sensor 10 includes a base portion 12attached to one portion of a vehicle, such as the portion of a shockabsorber 13 attached to the vehicle chassis 14, and a tracking portion15 which is attached to a portion of the vehicle whose position it isdesired to sense, such as the portion 16 of the shock absorber attachedto a wheel support assembly 17 (FIG. 1). The base and tracking portions12, 15 are relatively longitudinally moveable with respect to each otherand are external to the shock absorber 13.

The position sensor 10 further includes a housing 20 that supportscircuitry for generating position indicating signals and transmittingthose signals via a cable 22 to a vehicle ride control computer. In apreferred design an electrical connector 23 (FIG. 2) attached to thecable 22 is adapted to engage a mating connector (not shown) forconnection to a ride control computer and provides input and outputinterconnection for the position sensor 10.

A flexible cylindrical bellows 26 is coupled at one end to the baseportion and at an opposite end to the tracking portion of the sensor 10and defines an internal chamber 26a (FIG. 2). A winding assembly 32extends from the base portion 12 into a region surrounded by the bellows26. The winding assembly 32 includes a proximal end portion 34 fixed tothe sensor base portion 12 and a distal sensing portion positionedwithin the bellows 26.

The tracking portion 15 includes a support 40 for a transformer couplingmember that includes an elongated tubular conductor 43. The tubularconductor 43 has an inner diameter selected to freely slide over anouter diameter of the winding assembly 32. The support 40 includes afitting 42a for attachment of the tracking portion 15 of the sensor to amounting stud 45 of the shock absorber. A similarly constructed fitting42b at the base portion 12 of the sensor 10 allows the sensor 10 to beattached to a second mounting stud 45 attached to the shock absorber.

The winding assembly 32 includes a primary winding 44 and a secondarywinding 46 that are mutually suspended in a material 48 within a plasticcasing 49. This material 48 acts to damper shock and vibration. Theprimary and secondary windings 44, 46 are aligned side-by-side, forsubstantially their entire length and are generally mutually paralleland spaced apart. The primary winding 44 includes an elongatedcylindrical core 50 and a coil 52 defined by a single magnet wirespirally wound around the core 50 over substantially the entire lengthof the core. The secondary winding 46 includes an elongated cylindricalcore 54 having a coil 56 defined by a single magnet wire spirally woundaround core 54 over substantially its entire length.

The FIG. 1 embodiment can be constructed using 0.045 inch diameterferromagnetic steel alloy 45a (for the primary), 4140 (for thesecondary) welding rods. In a presently preferred embodiment of theinvention, steel alloy 41L40, cold drawn "annealed in process" rods areused for both the secondary and primary cores. These rods are preferablyinsulated with a 0.0012 inch layer of cathodic electro-deposition primer(A Class, Surface E Coat) coating. Their lengths are 4.39 inch. Thecoils use 39 gauge solderable polyester coated, magnet wire. The coil isthen covered by a protective film varnish Dolph AC43.

The proximal end 34 of the winding assembly 32 for includes a plasticcarrier 51 (FIG. 7) that carries metal terminals 53a-53d for routingenergization signals to the primary winding 44 and output signals fromthe secondary winding 46. The carrier 51 is constructed from plastic(preferably 30% glass reinforced polyester) and is molded to form rightand left carrier halves. Each half defines an opening 55 into which thecylindrical cores 50, 54 are pressfit. The wire coils 52, 56 are thenwound around the cores 50, 54 and attached to their respective terminalsbefore the insulator such as a mylar sleeve is slipped over the coils.The two halves of the carrier 51 are then attached together and thecores 50, 54 are suspended in the suspension material 48. To suspend thewindings 44, 46 the cylindrical sheath 49 is filled with the suspensionmaterial by pouring the material into an inner cavity of the sheath 49.An end cap or plug 53 is pressed into a distal end of the sheath 49. Thecompleted winding assembly 32 is then pushed into the base portion 12 ofthe sensor until the carrier 51 seats within a cavity in the baseportion 12. A plastic cover 55 that includes the fitting 42b is thenconnected to the base portion 12 to fix the winding assembly 32 inplace.

The bellows 26 engages similarly configured circular slots or grooves57, 59 defined by the base and tracking portions 12, 15 respectively andinhibits dirt and the like from entering the sliding interface betweenthe support 40 and the base portion 12. During installation the trackingportion 15 is attached to the shock absorber via the fitting 42a andstud connection. The bellows 26 is attached to the tracking portion 15and the base portion so the winding assembly 32 fits within theconductor 43. The base portion 12 is then attached to the stud 45 viathe fitting 42b and the bellows attached to the base portion by pushingthe bellows over the base portion 12 until ridges of the bellows seat inthe grooves 57.

When the sensor 10 is installed the tubular conductor 43 (3003 aluminumalloy, half hardened) surrounds a varying length of the coextensive,spaced, parallel primary and secondary windings 44, 46 and provides atransformer coupling adjustment member for the windings, which areconfigured as a transformer. In the embodiment illustrated in FIGS. 1-4,the tubular conductor 43 is a transformer coupling enhancing memberwhich increases the transformer coupling between the primary andsecondary windings as the primary and secondary windings and tubularconductor 43 become more telescopingly coextensive, as a result ofmovement of the vehicle wheel assembly 17 closer to the vehicle frame14.

In the illustrated embodiment, the tubular conductor 43 is a nonferrousmetal, such as aluminum, which enhances transformer coupling between theprimary and secondary windings 44, 46 through a looping current that isdeveloped in the tubular conductor 43 as a result of excitation of theprimary winding 44.

Sample results obtained from uniformly wound primary and secondary coilsare illustrated in FIG. 9. By reference to this figure, it is seen thatthe signal developed across the secondary winding, which is directlyproportional to the voltage transfer ratio, is substantially linearlyrelated to the amount of overlap of the tubular conductor 43 withrespect to the sensing or distal portion of the winding assembly 32.

An important feature of the present invention is that the spirally woundcoils may be wound with a pre-established non-constant turn spacing, bya commercially available numerically controlled winding apparatus, in amanner that may substantially cancel any remaining nonlinearity and iswithin the capabilities of one skilled in the art. Alternatively, it maybe desired to provide a particular characteristic nonlinear voltagetransfer ratio for a particular application. The turn density may bearranged in order to "tune" the voltage transfer ratio to the desiredcharacteristic.

In an alternate embodiment of the winding assembly (FIGS. 5 and 6) thesuspension material is eliminated and the shell material 48 is extendedto secure and provide structural stability to the winding assembly.

The FIG. 5 and 6 embodiment has cores 50 and 54 that are 0.45 inch indiameter steel alloy 41L40 rods insulated with a 0.0012 inch layer ofcathodic electrodeposition primer (A Class, Surface E Coat) coating orother insulating material and are 7.2 inches in length. Coils 52 and 56include a double layer of 41-AWG and 43-AWG wire, respectively,compactly wound on the associated insulated core which produces aninductance of 3 to 4 milihenries for each coil. Primary and secondarywindings 44 and 46 are each covered by a protective film such as a Mylarsleeve (not shown), and are mutually encapsulated by an appropriatematerial 48 which, in the illustrated embodiment is a liquid crystalpolymer, such as Celanese Corporation Vectra B-130.

With reference to FIG. 10, organization of a control circuit 28 mountedto a printed circuit board 61 carried by the housing 20 will bedescribed. A square wave generator 58 produces a square wave signal onits output line 60. The square wave signal, which operates at 12.8 KHzin the illustrated embodiment, is provided as an input to a sine waveshaper circuit 62 which converts the square wave signal to alow-harmonic distortion sine wave signal having the same frequency whichis provided on its output 64. The sine wave signal is amplified by anamplifier and driver circuit 66 and provided at an output 67 to theprimary winding 44 of the winding assembly 32. The sine wave signalprovided to the primary winding is coupled to the secondary winding inproportion to the relative longitudinal overlap of the winding assembly32 and the coupling member 42. The signal developed across the secondarywinding is provided on an output 68 to a buffer amplifier 70, whichprovides a high input impedance for and amplifies the relatively smallsignal developed across the secondary winding. Buffer amplifier 70additionally includes means for eliminating induced high frequency noiseand any DC offset. The output 72 of the buffer amplifier is provided toa precision rectifier 74 which produces a DC analog voltage on itsoutput 76, proportional to the average AC voltage developed across thesecondary winding. The DC analog voltage is amplified by a DC amplifier78 and provided by an output 80 as an input to a ride control computerof the vehicle (not shown).

The output 60 of the square wave generator 58 is additionally providedas an input 81 to a negative power source 82 which produces a voltage onits output 83 which is negative with respect to the vehicle chassisground and is provided as an additional supply voltage to the precisionrectifier 74 and the DC amplifier 78. The purpose of supplying theseportions of the control module with a negative voltage, which isnormally not available in a vehicle electrical system, in addition tothe conventional positive supply voltage, is to improve the linearity ofthe output signal, especially at low signal levels, while allowing theDC offset of the sensor output to be adjusted to a desired level, whichmay be zero or even a negative voltage. Additionally, by supplying avoltage to the precision rectifier and the DC amplifier that is negativewith respect to chassis ground, means are provided for detecting certaininternal failures of these circuit portions by monitoring the polarityof the voltage on the output 80. If the polarity of the output becomesmore negative than a predetermined level, an indication is provided tothe ride control computer that the position sensor is malfunctioning.

A detailed description of this embodiment of the electrical controlsystem is provided by reference to FIG. 11. The vehicle supply voltageis connected through a connector to an input 85 and is conditioned by aninput filter 86 and a reverse polarity protection diode 88. Theconditioned supply voltage is regulated to a constant voltage VCC by avoltage regulation means 90, which may be of any such means well-knownin the art and is illustrated as a programmable zener diode. The voltageVCC is produced on a bus 92 and is provided as a supply voltage toselected components in the circuit.

A square wave oscillator 58, in the illustrated embodiment, is a type555 CMOS timer 94 having a frequency established at 12.8 KHz by acapacitor 96 connected between a timing terminal of timer 94 and signalground and in series connection with resistors 97-100 and VCC bus 92.One of the resistors 100 is adjustable to provide factory adjustment ofthe frequency of timer 94. As is recognized by one skilled in the art,CMOS timer 94 provides a stable frequency and amplitude source over awide range of temperature conditions. The output (pin 3) from timer 94on line 60 is scaled by a pair of precision resistors 101 and 102,connected in a voltage divider arrangement, and provided on line 104.Line 104 is provided as an input 64 to amplifier and driver circuit 66through a resistor 106. The characteristics of the signal on line 104are significantly altered by sine wave shaper 62 which is connectedbetween line 104 and ground and serves as an "active load" low-passfilter to shunt the high frequency harmonics of the square wave signalto ground. This allows substantially only the low frequency component ofthe square wave, which is a sine wave having a frequency equal to thepulse repetition rate of the square wave generator, to pass to theprimary winding 44.

Sine wave shaper 62 includes an operational amplifier 108 having anon-inverting input on line 110 held at a constant voltage provided by avoltage divider consisting of resistors 112 and 114 series connectedbetween a positive DC power source V+ and signal ground. Amplifier 108further includes an inverting input 116 connected with line 104 througha capacitor 118. Amplifier 108 produces an output on a line 120, whichis connected with inverting input 116 through a resistor 122 and withline 104 through a capacitor 124. The particular configuration for sinewave shaper 62 causes it to actively shunt higher frequency componentsof the square wave to ground by the particular feedback arrangementbetween output line 120 and inverting input 116 including resistor 122and capacitors 118 and 124, while providing a relatively high impedanceto the base frequency of the square wave produced by timer 94 andserving to shape the signal. Accordingly, the resulting signal is a sinewave having a frequency equal to that of the pulse repetition rate oftimer 94.

The sine wave signal is provided through a resistor 106 to line 64 as aninput to amplifier and driver 66. Amplifier and driver 66 includes anoperational amplifier 126 having a non-inverting input 128 provided witha constant voltage level from the voltage divider formed by resistors112 and 114 and an inverting input 130 connected with input line 64 andprovided with the sinusoidal signal previously described. Amplifier 126includes an output 132 connected directly with the base terminal of atransistor 134 whose collector is connected directly with V+ and whoseemitter is connected with a line 136. A feedback resistor 138 connectsline 136 with inverting input 130 to establish the combined gain ofamplifier 126 and transistor 134 and to cause this combination tooperate as a linear amplifier. A resistor 139 between line 136 andsignal ground provides a load for amplifier 126 and provides noisesuppression of high frequency signals induced from external sources.

Line 136 is connected to a parallel combination of a resistor 140 and acapacitor 142. The purpose of the parallel combination is to reduce theDC component of the signal provided to the primary winding 44 whilecoupling the AC component of the signal to the primary winding 44.Resistor 140 may be a varistor in order to compensate for the effect oftemperature variations of the DC resistance of primary winding 44. Theparallel combination of capacitor 142 and resistor 140 are connectedthrough a filter circuit 144 to one terminal of primary winding 44, theother terminal of which is connected to signal ground.

The excitation of primary winding 44, by the previously describedcircuitry, creates a magnetic flux which is coupled by the transformercoupling member 42 to the secondary winding 46 which will cause a signalto develop across the secondary winding. The secondary winding 46 isconnected between line 68 and signal ground. Line 68 is connected to oneterminal of a series capacitor 146 in order to couple only the ACcomponents of the signal developed across secondary winding 46 to theremaining portions of the circuit. A second terminal 149 of capacitor146 is connected to a capacitor 148 which provides a high frequencyshunt to ground to reduce high frequency noise induced into the windings44, 46. Terminal 149 is connected to the input of buffer amplifier 70through a series combination of a gain-adjusting resistor 150 and aresistor 152.

The buffer amplifier 70 includes an amplifier 156 having an invertinginput 154 to receive the signal from resistor 152. Amplifier 156 furtherhas a non-inverting input 158 connected to a constant voltage source,provided by a voltage divider consisting of resistors 160 and 162connected in series between V+ and signal ground in order to impart afixed DC bias to the signal. A feedback circuit, consisting of aparallel combination of a resistor 164 and capacitor 166, is connectedbetween output 168 of the amplifier and its inverting input 154. In thisconfiguration, buffer amplifier 70 provides a high input impedance forthe low signal level developed across the secondary winding 46 andamplifies the signal. The output of the amplifier 70 is AC coupled by aseries capacitor 170 and a resistor 178 to an input 72 of the precisionrectifier 74.

The precision rectifier 74 includes an operational amplifier 172 havinga non-inverting input 174 connected to ground through a resistor 175. Aninverting input 176 is coupled to the signal on the line 72. A diode 180is provided as a feedback path between an output 182 and input 176 ofamplifier 172 and serves to cause amplifier 172 to conduct positivegoing portions of the AC signal seen at the secondary of the transformerbut to not conduct the negative going portions. In addition, output 182is further connected through a forward biased diode 184 and a resistor186 to output line 76. Diode 184 is additionally connected to invertinginput 176 through a resistor 188. This configuration provides a forwardvoltage drop that is substantially reduced from that of a conventionalrectifier by essentially dividing the forward voltage drop by the openloop gain of amplifier 172. Additionally, this configuration providesexceptional temperature stability through the use of a pair ofoppositely poled diodes in the feedback loop.

Line 76 from the precision rectifier 74 is provided to DC amplifier 78,which includes an amplifier 190. Output 76 is connected to thenon-inverting input of amplifier 190. An inverting input 192 ofamplifier 190 is connected through a series resistor 194 to a voltagedivider consisting of resistor 195, 196, 197, and 198 serially connectedbetween VCC and signal ground. Resistor 197 is adjustable and providesmeans for adjusting the DC offset on the output of amplifier 190, whichis provided on line 199. A parallel combination of a resistor 200 and acapacitor 202 is connected as a feedback path between output 199 andinverting input 192 and establishes the gain characteristics ofamplifier 190 while providing low pass filtering characteristics toreduce AC ripple on output line 199. Output 199 of DC amplifier 78 isconnected through a resistor 204 to output line 80 which is, in turn,connected to an output pin 206 of connector 29. A diode 208 betweenoutput line 80 and signal ground provides a reverse voltage clamp toeliminate excessive negative voltage swings that otherwise could bepassed to the ride control computer. Additional low pass outputfiltering is provided by capacitors 209 and 210.

Output 60 of square wave generator 58 is additionally connected to thenon-inverting input of an amplifier 212 whose inverting input 214 ismaintained at a constant voltage level by voltage divider comprisingresistors 216 and 218 connected in series between VCC and ground.Amplifier 212 provides a low impedance source for providing a cyclicallyvarying signal to a rectifier circuit 82 including series capacitor 220,series diode 222, shunt diode 224, and shunt capacitor 226. The outputof rectifier circuit 82 is provided on line 82 as a DC voltage which isnegative with respect to signal ground. Negative voltage line 83 isprovided as a supply voltage to amplifiers 172 and 190 in addition tothe positive voltage supplied to these amplifiers from V+. In thismanner, amplifiers 172 and 190 are capable of operating in a linearregion even at small signal levels and the DC offset on output line 199of amplifier 190 may be adjustable to zero and even a negative voltage,if desire. An additional advantage of providing a negative voltagesupply to amplifiers 172 and 190 is that an internal failure of eitheramplifier may result in a negative voltage in output line 199 whichcould be interpreted by the ride control computer as an indication of amalfunctioning of the control module.

Operation

In operation, a square wave of stable frequency and amplitude isproduced by square wave generator 58 on line 60, which includes a lowfrequency component and harmonically-related higher frequencycomponents, and is scaled by resistors 101 and 102. The scaled squarewave is converted to a low-distortion sine wave by the activeload, highfrequency shunt action of sine wave shaper 62. Sine wave shaper 62provides a low-impedance shunt for the higher frequency components and ahigh-impedance load to the low frequency signal component of the squarewave, as well as serves to refine the shape of the resulting signal.Therefore, a low distortion, stable amplitude sine wave is produced.This sine wave signal is amplified by amplifier and driver 66 and isprovided to primary winding 44 through resistor 140, capacitor 142, andfilter 144.

The excitation of primary winding 44 induces a spirally looping currentin tubular conductor 43. In turn, the looping current in the tubularconductor 43 causes a voltage to be induced in the secondary winding 46that is proportional to the length of the winding assembly distalportion that is telescoped within the tubular conductor 43. Thus, thetubular conductor 43 provides the transformer coupling between theprimary and secondary windings. The voltage developed across secondarywinding 46 is amplified by buffer amplifier 70 and rectified to a DClevel, equal to the average value of the AC signal, by precisionrectifier 74. The output of precision rectifier 74 is amplified andfurther filter by amplifier 78. The gain of the control module may beadjusted by adjusting resistor 150 and the offset of the output signalon pin 206 may be adjusted by adjusting resistor 197.

The effect of the tubular conductor 43 of the sensing portion of thewinding assembly is illustrated by reference to FIG. 12, in which:

K represents the forward voltage transfer ratio

R is the effective input resistance of the sensor

X is the effective sensor input reactance

V₁ is the input voltage signal provided to the primary winding 44

V₂ is the output voltage signal developed across the secondary winding46.

I_(S) is the looping current induced in tubular conductor 43.

Windings 44 and 46 are long, slender coils. A current in such a coilcauses a magnetic flux that is dense inside the coil and decreases withdistance rapidly outside of the coil. Therefore, except for the effectof tubular conductor 43, essentially no signal V₂ would be developedacross winding 46 in response to the excitation of winding 44 becausethe windings are side-by-side. As tubular portion 42 overlaps a portionof the winding assembly, the magnetic flux produced by the primarywinding links the tube, which induces a looping current in the tube.This induced current produces a flux within the tube, which is oppositeto and partially cancels the primary flux. If the counter-flux is, forexample. 0.3 times the original flux in the primary coil, the fluxwithin the primary coil will be at its original amplitude within thenon-overlapped length, but at only 70% of its original amplitude withinthe overlapping portion. This will reduce both R and X, which willrespond as though the overlapped portion of the primary winding werepartially shorted, or removed from the circuit.

Since the same length of secondary winding 46 is within the tubularconductor 43, this portion of the secondary winding will experience, inthis example, a flux that is 30% of the original flux amplitude in theprimary while the non-covered portion of the secondary will experienceessentially no flux. V₂ is directly proportional to V₁ times the ratioof flux in the secondary to the flux produced by the primary. The resultis a voltage induced across the secondary that is proportional to thelength of the winding assembly that is within the tubular portion 42.

In the preferred design illustrated in FIGS. 1-11 the coupling member isconstructed from a conductive tube, preferably aluminum. The windingassembly 32 fits within the confines of the tubular conductor 43 to agreater or lesser extent depending upon the relative positioning of thewheel assembly and vehicle chassis.

In FIG. 13, an alternate design is shown wherein the winding assembly 32is of the same construction but wherein a relatively short annularcoupling member 250 surrounds a portion of the winding assembly 32 andmoves in relation to the winding assembly 32 to cause a positionsensitive output signal. In this short coupling design, as relativemovement occurs between the coupler 250 and the winding assembly 32, thecoupler overlies a constant length of the primary 44 and secondary 46windings. In the design having a constant turn density for the primaryand the secondary the output signal from the secondary would thereforeremain unaffected by back and forth movement of the member 250.

To produce a meaningful output from the secondary 46 in response torelative movement between the coupler 250 and the winding assembly 32, avariable turn density is incorporated as the primary 44 is wound. Thisis depicted in FIGS. 24 and 25 wherein the turn density is adjusted. Inthe FIGS. 24 and 25 depictions the windings 52 are also spaced from thecore by an insulating sleeve 50a that is applied to or slipped over thecore 50. This results in a variable flux produced by the primary alongthe length of the primary 44 producing a variation in the couplingbetween the primary and secondary coils based on the position of thecoupling member 250. By varying the turn density in accordance with afunctional relation N_(p) (x) it is possible to achieve a desired fluxprofile along the length of the winding assembly 32. An example of thesecondary output signal produced by the arrangement depicted in FIG. 13is seen in FIG. 21. The data in this figure was obtained by measuringthe induced EMF on the coupling member 250 based upon a variable turndensity in the primary 44. Since the induced EMF in the secondary isdirectly related to the induced EMF in the coupling member 250, asimilar output from the secondary coil 46 would be expected.

In addition to varying the turn density along the primary coil 44 it ispossible that the turn density of the secondary 46 be varied. In thisinstance, the induced EMF in the coupling member 250 is uniform but theinduced EMF in the secondary varies with turn density. FIG. 22illustrates an example of the output from the secondary winding 46 as afunction of coupler position along the length of the constant densityprimary 44. In this example, the length of the coupling member 250 isvery much shorter than the lengths of the primary and secondary coils44, 46. Specifically, the primary and secondary had lengths greater than6 inches and the coupling member 250 had a length of approximately 1/4inch.

The choice of the turn density variation is not limited to the primaryand secondary coils. Instead of a solid conductor, a variable turndensity coil could be wound on a form and used to construct theelongated coupling member 250.

In addition, any achievable variation in turn density is possible and inparticular it is possible to tailor the turn densities so that aspecific critical location of the coupler member 250 with respect to theprimary and secondary coils can be chosen to produce a peak outputsignal or alternately can be chosen to produce a rapidly changing outputsignal for triggering an output from suitable sensing electronics.

Furthermore, instead of coil windings, conductive patterns can beetched, scribed or deposited on a form for each of the primary,secondary, or coupling members. This alternative is depicted in FIGS. 26and 27 wherein the coil 252 is produced by etching or scribing aconductive layer or alternatively deposited onto (using a screeningtechnique) an insulator 254 that covers a magnetically permeable core256.

Theoretical Model

In comparing the short and long conductive coupling members 43, 250 ofFIGS. 2 and 13 the long coupling member 43 can be thought of as many ofthe short couplers placed colinearly. In a device of this nature theinductance of the coupler and it's effect on the primary are small witha short coupler and more pronounced in an extended one.

Each of the turns of wire on the primary creates a flux distributionalong the core on which the wire is wound. This flux distribution hasthe following characteristics:

A) The flux intensity due to a given turn of wire monotonicallydecreases in intensity as distance along the core from the turn of wireincreases.

B) The flux intensity profile along the core due to a given turn of wireis symmetric about the position of the wire except near the ends of thecore. Near the ends of the core the flux distribution falls off morerapidly near and beyond the end of the core than it would 5 mm in fromthe end of the core.

C) At representative currents (≦50 mA), turn densities (≦300/inch) andfrequencies (around 13 KHz), the flux from 1 turn of wire is independentof the flux from another. In other words a turn in a high turn density(100-300 turns/inch) region behaves the same as a turn of wire in a lowdensity region (20-30 turns/inch).

However, due to the intrinsic limits on linearity in magnetic materials(hysteresis, variable permeability) the behavior of turns of wire withinhigh and low turn density regions cannot be identical. Note that withinobserved frequency-current-turn density values such variations ofbehavior can be neglected. However, in some cases it may be necessary todetermine corrections in an iterative approach.

With these characteristics in mind a model can be constructed where eachturn of wire on the primary makes a position dependent contribution tothe flux linking the coupling member. The combined flux contributionsfrom all turns of wire linking the coupling member then induce eddycurrents in the coupling member which generates flux and induces asignal on the secondary. In the data depicted in FIG. 23 a 5 mm longsingle turn coil (conducting aluminum tube) was used in conjunction withprimaries and secondaries that were divided into 1.25 mm long turndensity elements. Within each density element the turn density was heldconstant while being allowed to vary between elements.

In FIG. 23 a voltage profile ("secondary voltage") is shown for aprimary coupled to a secondary through a short coupling member. Thecoupling member was slowly moved along the length of the coils. Theprimary consisted of 58 turn density elements and had a total length of72.5 mm. The secondary consisted of 104 turn density elements with atotal length of 130 mm. As can be seen in the figure the turn density ofthe primary was rapidly varying while that of the secondary was heldconstant. In the region where the primary turn density is zero (i.e. theregion of no overlap of primary and secondary) the secondary voltage isseen to drop dramatically. Additionally, the voltage is seen to varymore slowly than the actual turn density variation. With the constantdensity secondary extending >3/4" beyond the ends of the variabledensity primary, it was assumed that all secondary voltage variationwould be due to the variation in the primary. A parametric model linkingvoltage to primary turn density variation was constructed as follows:##EQU3## where A is an additive constant representing background (noncoupler induced) coupling, P_(n) are weighing coefficients, DP_(n) arethe primary turn densities and Φ is the primary current. A least squaresfit is applied to the data against this model and over 20 monotonicallydecreasing coefficients (P_(a)) are found.

A similar model is used when the secondary turn density varies and acombined model is used when both primary and secondary turn densitiesvary. In this combined model the flux created by the eddy currents inthe coupling member extends symmetrically from the position of thecoupling member (except near the ends of the cores) and links each turnof the secondary in proportion to the strength of the coupling member'sflux at the position of the turn of wire. The combined model is of theform: ##EQU4## where P_(n), S_(n), DP_(n), and DS_(n) are primary andsecondary weighing coefficients, primary and secondary turn densities, Cis an additive constant, and "O" and "G" vary from coil to coil. Byadjusting these factors for manufacturing repeatability, thistheoretical model can be used to predict secondary voltage ("V_(sec) ")to within an offset ("O") and a gain ("G"). It is noted that thecoefficients that are calculated using the least squares fittingtechnique vary with changes in core materials and diameters and withchanges to coupler length and/or materials. Additionally, the P_(n) andS_(n) have temperature dependence resulting in P_(n) →P_(n) (t) andS_(n) →S_(n) (t). Temperature variations become less important, however,with appropriate material choices for the cores and coupling member.

The "1st pass" error between measured and predicted voltages is under3%. The model is "incremental" as opposed to "continuous." In a"continuous" model P_(n) (t)→P(x,t), DP_(n) →DP(x), S_(n) (t)→S(x,t),DS_(n) →DS(x), and the summations become integrals and eddy currentvariations along the coupler can be accounted for in an additionalintegration over the length of the coupler. This will allow higheraccuracies in predicted versus actual secondary voltage outputs. Thedisclosed model is incorporated in a least squares fitting routine topredict the primary and secondary turn densities required to achieve agiven "V_(sec) " vs. "X" response for a given use of the invention.

FIG. 14 illustrates still another alternate use of a short couplingmember 250. In this example, the winding assembly 32 defines an arcuateor curved member and the coupling member 250 is mounted for movementalong an arcuate path. Rather than define the position of the couplingmember 250 in terms of position "x" along the length of the windingassembly 32, it is appropriate in such a configuration to consider theangular position of the coupling member 250 along the arcuate pathdefined by the winding assembly 32. Rather than plot coupler position ininches and secondary output in volts, it is then appropriate to refer tothe coupler position in radians with respect to a reference orientationor angle.

In the preferred embodiment of the invention, the primary and secondarywindings 44, 46 are wound around cylindrical cores 50, 54. Theencapsulating shield 49 for the assembly 32 is also cylindrical. InFIGS. 15A-15C, alternate shapes for the cores 50a 54a, 50b 54b, and 50c54c are depicted. In FIG. 15A the support for the cores 50a, 54a is ovalin section; in FIG. 15B it is rectangular, and in FIG. 15C the cores arearranged about an arc. The coupling members 250 used with theseembodiments having inwardly facing surfaces that conform generally tothe encapsulating material. This is not a requirement, however, and arectangular coupling member could be used, for example, with the ovalshaped core support in FIG. 15A.

It is readily apparent that the production of a signal output thatvaries as a function of position can be achieved in a variety of ways.If one were to vary the diameter of the magnetically permeable cores 50,54 along their length, for example, as shown in FIG. 49, the signaloutput as a function of position could be controllably adjusted.Similarly, if the magnetic material content of a winding core is changedalong its length, as shown in FIG. 50, the signal output as a functionof position can be controllably adjusted. In FIG. 32 the shape and/orthe wall thickness of the coupling member 250 can also be varied as afunction of position along its length. This also produces a positionsensitive change in coupling between the primary and the secondary.

FIGS. 28 and 29 illustrate an alternate design wherein the couplingmember comprises a compressible bellows 252 that is mounted relative tothe primary and secondary windings 44, 46. An electrically conductiveplating is applied to the bellows and the bellows 252 is attached tomove with one of the relatively moveable members. As the bellows 252compresses and expands, the transformer coupling between the primary andthe secondary will change and a signal output from the secondary willvary with the relative position of the relatively moveable numbers.

FIGS. 30 and 31 illustrate a similar design. In this design, the bellows252 is replaced by a conductive spring 254 that compresses and expandsand is used to adjust transformer coupling between the primary andsecondary 44, 46.

FIGS. 33-35 illustrate an alternate embodiment wherein parallel, primaryand secondary windings 260, 262 are spaced in a side-by-side arrangementand a cylindrical shield 264 moved in and out to overlap a variableportion of the secondary. This modifies transformer coupling between theprimary 260 and secondary 262. The shield 264 could be used to interruptmultiple secondaries as well. As the moveable shield 264 becomes moreextensive with the primary, the signal output from the secondarydecreases. This same decrease in signal output would occur for allsecondary signals wherein multiple secondaries are used. It is alsopossible to selectively shield secondaries and leave others unshielded.Other adjustments are possible by control over the winding density toprovide a desired output verses displacement correlation. As depicted inFIGS. 33-35, the shield 264 and primary and secondary windings 260, 262are surrounded by a casing 266 which protects the primary and secondary.When the casing is electrically conductive, it enhances the couplingbetween the primary and secondary(s). This serves to increase the signalswing between positions where the moveable shield 264 is fully insertedand when it is fully withdrawn. An electrically conductive case alsoserves to shield against signals induced by external electric fieldsources. A magnetically permeable case shields against external magneticfield sources. In a preferred embodiment, the case is highlyelectrically conductive and highly magnetically permeable such as usingCMI steel or CMI steel with copper plating or tubing.

Turning now to FIGS. 36-38, an alternate embodiment of the invention isdepicted where the primary and secondary are not fixed with respect toeach other, but instead one winding 270, for example, is fixed inrelation to a cylindrical spoiler (coupler) 272 while the other winding274 moves relative to the first. This embodiment experiences somedisadvantages in fabrication, but is feasible. In this case the windingalone may be withdrawn or the winding plus the core. Preferably, thewinding only would be withdrawn to diminish signal pick-up from externalelectro-magnetic field sources.

An additional modification to the above-mentioned alternative is aconfiguration shown in FIGS. 39-41 where the windings 280, 282 are fixedand a center core 284 about which one winding is wound can be moved intoand out of the coils to adjust the coil coupling. In such an embodiment,the coils are preferably wound on insulated bobbins to increasereliability. Additionally, in this embodiment, different diameter coreshaving different permeabilities along their length could be utilized.

FIGS. 51-53 illustrate a movement sensor 290 wherein primary andsecondary windings 44, 46 are fixed to a flat plate 292 connected to oneof two moveable members. A semi-cylindrical shield 294 is coupled to asecond of the relatively moveable members. Unlike all the other couplersthe shield 294 does not provide a closed electrical path for inducededdy currents that completely encircles both of the members. A tongueand groove engagement between the plate 292 and shield 294 allowstranslation of one with respect to the other. As variable portions ofthe shield 294 overlie the primary and secondary 44, 46, the transformercoupling changes and therefore an indication of relative position of thetwo moveable members is provided from the secondary.

Alternative Coupling Embodiment

In accordance with an alternate embodiment of the invention shown inFIGS. 16-18 the primary and secondary windings are positioned one withinthe other and separated by a cavity, or gap, and a coupling adjustmentmeans includes a coupling disrupter member longitudinally positionablebetween the windings in the gap. In this embodiment, as the couplingadjustment means and the sensing probe become more telescopinglycoextensive, the voltage developed across the secondary winding, as aresult of the voltage applied to the primary winding, decreases becausethe coupling adjustment means inhibits, or reduces, the amount oftransformer coupling between the windings.

In this embodiment, a non-contact linear position sensor assembly 310includes a base portion 312 and a tracking portion 316, which aremutually longitudinally telescopingly positionable with respect to eachother. Base portion 312 includes attachment means (not shown) forattachment thereof to a stationary portion of the vehicle and trackingportion 316 includes attachment means 318 for attachment to a moveableportion of the vehicle, such as a wheel assembly. Base portion 312includes a sensing portion 336 including a primary winding 344comprising a coil 352 spirally wound around the axis of the core 350(FIGS. 16, 17, and 18). Primary winding 344 is seen to be positionedwithin a secondary winding 346 which includes a core 354 having a walldefining a central bore that has an inner diameter that is substantiallylarger than the outer diameter of core 350. Secondary winding 346further includes a coil 356 wound about the axis of the core 354. Thedimensions of the primary and secondary windings are selected in orderto define a cavity or gap 338 between the primary and secondarywindings. A tubular portion 342 of tracking portion 316 islongitudinally positionable within the gap 338. Tubular portion 342 andsensing portion 336 define a sensing probe 335.

Core 350 includes an enlarged end portion 334 which is sized tofrictionally engage core 354 which, in turn, is sized to frictionallyengage a frame member 326 included in base portion 312 (FIG. 16).Position sensor 310 further includes a stress relief member 230 whichengages frame 326 and supports a plurality of electrical leads extendingto a control module 328 which, in turn, is connected by an electricalconnector 329 to the ride control computer (not shown).

Core 350 is made from a ferromagnetic material, such as iron, and thesecondary core 354 is made from a non-magnetic material, such as astructural polymer. As best seen in FIG. 16, the primary and secondarycoils do not extend the entire length of their respective cores. Rather,the coils are positioned on their respective cores in a manner that willprovide interface between the coupling means and the coils over theentire extent of travel of tubular portion 342, plus an additionallength of the core equal to approximately 10 percent of the innerprimary coil and 5 percent of the outer secondary coil. Primary andsecondary windings are each spirally wound around their respective coresfrom a single length of wire and are each covered by a protective filmsuch as Mylar sleeve or other insulating material.

Because primary winding 344 is positioned within secondary units 346,excitation of the primary winding by a voltage V₁ induces a voltage V₂in the secondary winding (FIG. 20). The coupling adjustment member inthis embodiment, which is defined by tubular portion 342, operates as amagnetic shield which interrupts this transformer coupling betweenprimary winding 344 and secondary winding 346. Tubular portion 342creates a variable reluctance path for the magnetic flux. This variablereluctance path proportionately decreases the amount of current inducedinto the secondary winding. The flux available for inducing a voltage inthe secondary winding is proportional to the length of gap 338 in whichthe tubular portion 342 is absent. Accordingly, as tubular portion 342is additionally telescopingly extended within gap 338, the magneticshielding effect of the tubular portion reduces the magnetic couplingbetween the windings, which reduces the voltage developed across thesecondary winding from the signal applied to the primary winding.Therefore, the output signal from the sensing probe responds to therelative positioning of the position sensor portions in the oppositemanner to that described in the embodiment illustrated in FIGS. 1-10. Inthe illustrated embodiment, tubular portion 342 is made from a magneticmetal such as iron. However, nonferrous and even nonmagnetic materialscan be used for the tubing, particularly in the case where the materialsare electrically conductive. Alternately a shorted variable turn densitycoil on a non-electrically conductive tubular form can be used as well.Any material or coil and material combination can be used so long as thetubing has an effect on the transformer coupling.

The control module 328, provided with this embodiment, as illustrated inFIG. 11, is essentially the same as that disclosed in FIGS. 4 and 5,with the addition of an inverting amplifier 232 connected with theoutput 80 of DC amplifier 78. Inverting amplifier 232 includes anoperational amplifier 234 having a feedback resistor 236 extendingbetween an output 238 of the amplifier and an inverting input 240, inorder to establish its gain. The non-inverting input 241 of amplifier232 is provided with a constant voltage level through a voltage divider,comprising resistors 244, 245, and 246 series connected between VCC andground, and a series resistor 242. In the embodiment illustrated in FIG.11, resistor 245 is adjustable. Amplifier 234 is supplied with both apositive voltage V+ and a negative voltage, the latter from line 83. Theoperation of the control module illustrated in FIG. 19 is essentiallythe same as that illustrated in FIGS. 10 and 11. However, the output 80of amplifier 78 is further amplified and inverted due to the inclusionof an additional output stage including inverting amplifier 234.

Representative values of various components in the illustratedembodiment of the circuit of FIGS. 10 and 11 are as follows:

    ______________________________________                                        Reference Number   Value                                                      ______________________________________                                        Capacitor 96       .001 uf                                                    Resistor 97        1K                                                         Resistor 98        10K                                                        Resistor 99        41.2K                                                      Resistor 101       15K, 1%                                                    Resistor 102       5.11K, 1%                                                  Resistor 106       8.25K                                                      Resistor 112       75K                                                        Resistor 114       23.7K                                                      Capacitors 118, 124                                                                              0.0022 uf, NPO type                                        Resistor 122       10K, 1%                                                    Resistor 138       18.2K                                                      Resistor 139       68.1                                                       Resistor 140       301                                                        Capacitor 142      4.7 uf                                                     Capacitor 146      0.1 uf                                                     Capacitor 148      0.001 uf                                                   Resistor 152       118K                                                       Resistor 160       100K                                                       Resistor 162       100K                                                       Resistor 164       274K, 1%                                                   Capacitor 166      10 pf, NPO type                                            Capacitor 170      0.1 uf                                                     Resistor 175       1K                                                         Resistor 178       1K, 1%                                                     Resistor 186       47.5, 1%                                                   Resistor 188       2.1K, 1%                                                   Resistor 194       47.5K, 1%                                                  Resistor 195       4.06K                                                      Resistor 196       2.1K, 1%                                                   Resistor 198       200, 1%                                                    Resistor 200       274K, 1%                                                   Capacitor 202      680 pf                                                     Resistor 204       100                                                        Capacitor 209      1 uf                                                       Capacitor 210      0.001 uf                                                   Resistor 216       160K                                                       Resistor 218       200K                                                       Capacitor 220, 226 .47 uf                                                     ______________________________________                                    

Alternative Monitoring/Control Circuitry

In an alternate embodiment of the invention, the electronic conditioningcircuit 28 in the housing 20 is separated from the windings 44, 46 forpurposes of reducing size so the sensor 10 can be down-sized and placedin very tight application conditions. Such a control can be integratedwith vehicle anti-lock brake and traction control.

In an embodiment where the electronics are supported in a package inclose proximity to the coils, shielding of output signals is notnecessary. In an embodiment where they are separate, shielded coaxialcable is used to route output signals from the sensor 10 to theelectronics.

A control circuit 400 separate from the position sensor 10 is shown inFIG. 44 and includes a microprocessor 410 that is programmed with a userdefined algorithm stored in memory 412 and has a plurality of D/A drivechannels 414 and A/D detection channels 416. The channels will be usedto drive various sensors including the position sensor 10,condition/detect the sensor outputs, and pass the results on to anothercontroller.

Each drive channel will have a programmable or specifiable filterfollowed by a voltage, current or optical driver (op amps, LED or LaserDiode). Drive signals can include regulated voltages for other sensorsin addition to the necessary alternating current signals for multipleposition sensors 10.

Each detection channel 416 will consist of an amplifier or photodetector(op amp, PIN diode, etc.) followed by a programmable or specifiablefilter. Detected signals can include changes in d.c. voltage(potentiometric sensors), changes in a.c. amplitude for a positionsensor 10 or changes in intensity (optical sensors).

A given channel will be configured at point of manufacture by selectionof filter, drive and amplifier/detector types.

An alternate embodiment of the invention having multiple like sensorsuses one drive circuit to provide drive and/or signal conditioningcircuit for all probe assemblies. In this configuration, multipleprimaries are wired in parallel and driven with a single drive circuitlocated in the electronic control circuit.

In this alternate embodiment, a discrete signal conditioning circuit maybe provided for each secondary, or one signal conditioning circuit formultiple secondaries. In the latter instance, the signals from all thesecondaries are multiplexed and sent to the signal conditioning circuit.Multiplexing is a function internal to the electronic module. By havingthe electronic module provide one circuit to multiple probe assemblies,electrical components are reduced.

The use of a single microprocessor 410 eliminates redundant algorithmicsensor analyses conducted by more than one controller. The module actsas the central point for signal conditioning.

In operation the control unit would be used to drive a multiplicity ofsensors, displays, actuators and communicate with one or more othercontrollers. In an automotive sensing application the microprocessor 410could, for example, generate a digital signal for each sensor 10 andcommunicate the digital signal via an interface 420 to a body computer(not shown) which uses the sensor information to adjust the vehicleride. Other sensor inputs could be transmitted to other computers forcontrolling engine performance and the like. A user defined program inthe microprocessor 410 and the input/output channel configuration atpoint of assembly would allow the circuit to be configured for a broadnumber of uses.

Additional Sensors

Accelerometers may be incorporated with the sensor package or with theremote electronic module/probe assembly configuration. Packaging theaccelerometer with either sensor configuration is useful when a point ofmeasurement for position can be shared with a point of measurement foracceleration. As depicted in FIGS. 42 and 43, acceleration is measuredby a "stand alone" sensor 430.

The housing 20 containing the combined electronics and probe sensorsupports the accelerometer 430. The orientation of the accelerometer 430as it is mounted to the housing will determine the axis of accelerationmeasurement.

The preferred accelerometer utilizes a Kynar Piezo Film Accelerometerdesignated by part no. ACH-01 available from the Pennwalt Corporation.Necessary drive and/or signal conditioning circuitry for theaccelerometer can be provided within the electronic module 20.

When the sensing and drive electronics are remote from the probeassembly, an accelerometer can be supported by the probe assembly. Theprobe used in this arrangement has the advantage of measuring twoparameters (displacement and acceleration) at a single installationpoint. Wiring, in addition to what is between the probe assembly and thecircuit 400 is coupled between the accelerometer 430 and the electronicmodule 400. The circuit 400 would provide the necessary supply andsignal conditioning for the accelerometer 430. A more completedescription of the interface circuit required for the PennwaltAccelerometer is available in Pennwalt product brochure entitled"Accelerometer ACH-01" number 17 from the Kynar Piezo Film Department ofPennwalt, P.O. Box 799, Valley Forge, Penn.

It is possible to incorporate the accelerometer in the remote electronicmodule if the electronic module is installed at a point of accelerationmeasurement. As required, the electronic module can provide thenecessary supply and signal conditioning for the accelerometer.

Should the use of more than one accelerometer be required for multi-axismeasurements, the accelerometers can be implemented in the followingconfigurations:

Multiple accelerometers located in the original sensor package(containing electronics and probe in one housing) configuration andconnected to electronic module;

Multiple accelerometers located in the probe assembly housing of aseparate electronic module/probe assembly configuration;

Multiple accelerometers located in the electronic module housing of aseparate electronic module/probe assembly configuration; and

Multiple accelerometers packaged in an isolated housing but electricallyconnected to the electronic module of position sensor configurationsdescribe in the above.

The present invention lends itself to an application where both positionand velocity of two relatively moveable members are determined. Thefollowing describes a use of the sensor 10 to provide both position andvelocity. Additionally it is possible to cause the velocity response tovary with position or to have a nonlinear position vs. output response.The combined velocity/position sensor uses as a basis the FIG. 13embodiment of the invention. The windings of the secondary 46 are woundso as to produce a linear relationship in the flux linkage Φ_(v) (x)between the secondary and a short electrically conductive cylindricalpermanent magnet 250. The primary 44 is driven with a sinusoidallyvarying current and is wound so that the product of the amplitude of itsac flux linkage to the magnet 250 Φ_(pm) (x) and the ac flux linkage ofthe magnet to the secondary Φ_(ms) (x) varies linearly with position.The appropriate flux linkages are shown in FIG. 45.

In operation the primary is driven such that the highest frequencycomponent of the magnet's velocity is a decade below the frequency ofexcitation on the primary as shown in FIG. 46. As the magnet moves, anemf is induced on the secondary that is directly proportional to themagnet's velocity because:

    Φ.sub.v (x)=a*x+B=a*x(t)+B, which implies:

    Emf=-dΦ.sub.v (x)/dt=a*dx(t)/dt=a*v.

At the frequency of the primary excitation, an emf whose amplitude isdirectly proportional to the magnet's position is induced on thesecondary, via the normal operation principle of the sensor 10 discussedabove. The velocity signal is then obtained by low pass filteringfollowed by amplification of the secondary signal. The position signalis extracted by high pass filtering followed by amplitude demodulation.These signals are depicted in FIGS. 47 and 48. The separation infrequency of these two signals (before signal processing) is shown isFIG. 46.

In alternate embodiments the velocity signal is obtained from theprimary, made to vary with position according to a pre-defined functionand/or the position signal is made to vary from linear positiondependence according to a pre-defined function. Additional coils and/orcores can be incorporated and the magnet can be non-conductive with aconductive plating or insert. Finally, where the magnet has a conductiveinsert, the insert can be longer or shorter than the magnet to furtherdecouple the control mechanisms for the simultaneous variation of theposition and velocity signals, when necessary.

CONCLUSION

The present invention is readily adaptable to low cost automatedassembly. The windings may be spirally positioned on the respectivecores merely by rotating of the cores while applying the wire turns by anumerically controlled apparatus. The output characteristics of thesensor assembly, with respect to the relative positioning of the sensorprobe portions, may be adjusted by selectively adjusting theturn-spacing of the coils along various portions of the respective coresas shown in FIGS. 24 and 25. This versatility allows the position sensorto be "tuned" to the characteristics of a particular vehicle'ssuspension system. The ability to combine the packaging of the sensingprobe and electronic module allows adjustment to the electroniccircuitry, such as gain and offset, to be made at the factory before thecomponents are encapsulated. Thereafter, the position sensor assemblymay be easily positioned on the vehicle and connected to the ridecontrol computer without additional adjustment in the field. Thestructure of the various components additionally reduces weight and bulkand enhances the durability of the assembly. The unique aspects of thecontrol module according to the invention provides a reduced componentcount which further improves the compactness of the assembly and, alongwith the superior temperature stability of the circuit via its remoteconnection, allows an entire sensor probe to be positioned within aharsh environment. Furthermore, the components of the sensor probe canbe adapted for a lubricous sliding interfit provided by a hydraulicfluid of a shock absorber in which the sensor can be located with noeffect on sensor performance.

A linear position sensor assembly according to the invention may be maderesponsive over 90 percent of the stroke length of the tracking portionwith respect to the base portion. Thus, space occupied by the assemblyis substantially reduced. In addition to positioning within a shockabsorber, the invention may be adapted to mounting external to a shockabsorber parallel to the direction of its travel. The invention mayadditionally find application in sensing the position of portions of anautomotive vehicle other than the suspension system and may be appliedto non-vehicular uses such as use with machine tools and the like.

Other changes and modifications in the specifically describedembodiments can be carried out without departing from the principles ofthe invention which is intended to be limited only by the spirit orscope of the appended claims.

We claim:
 1. Position sensing apparatus for monitoring a relativeposition between two relatively moveable members comprising:a) anelongated field producing member coupled to a first of said moveablemembers and including a first multi-turn conductor would about a fieldproducing member axis and an input for energizing the first multi-turnconductor to produce an electromagnetic field in the vicinity of theelongated field producing member; b) an elongated field responsivemember fixed with respect to the elongated field producing memberincluding a second multi-turn conductor wound about a field responsivemember axis, said elongated field responsive member oriented in side byside, generally parallel orientation to the elongated field producingmember along a length of the elongated field producing member, andhaving an output for providing an output signal in response to theelectromagnetic field produced by the field producing member; c) acylindrical shielding member connected to a second of the moveablemembers for movement with the second moveable member and positionedgenerally co-axial with one member of the field producing and fieldresponsive members to overlap a portion of said one member that varieswith the relative position of the moveable members to alter the responseof the field responsive member as the moveable members move relative toeach other and thereby change the signal at the output of the fieldresponsive member; d) exciter means coupled to the input for energizingthe field producing member; and e) circuit means coupled to the outputfrom the field responsive member to correlate changes in the outputsignal with relative movement of the moveable members.
 2. The apparatusof claim 1 wherein said first and second multi-turn conductors areetched onto the field producing and field responsive membersrespectively.
 3. The apparatus of claim 1 wherein said first and secondmulti-turn conductors are scribed onto the field producing and fieldresponsive members respectively.
 4. The apparatus of claim 1 whereinsaid first and second multi-turn conductors are deposited onto the fieldproducing and field responsive members respectively.
 5. The apparatus ofclaim 1 wherein said field responsive members are oval in cross section.6. The apparatus of claim 1 wherein said field responsive members arepolygonal in cross section.
 7. The apparatus of claim 1 furthercomprising a cylindrical case that at least partially encloses the fieldproducing, field responsive and shielding members.
 8. The apparatus ofclaim 7 wherein the cylindrical case is electrically conductive toincrease coupling between the field producing and field responsivemembers, said apparatus producing a signal on the secondary thatincreases as the shielding member is withdrawn and decreases as theshielding member is inserted into the cylindrical case.
 9. The apparatusof claim 8 wherein the cylindrical case is highly magnetically permeableto provide shielding from the effects of magnetic field sources.
 10. Theapparatus of claim 7 wherein the case supports a shorted electric coilhaving a controlled turn density along its length and further whereinthe case is constructed from a material having a low magneticpermeability.
 11. Position sensing apparatus for monitoring a relativeposition between two relatively moveable members comprising:a) anelongated field producing member coupled to a first of said moveablemembers and including a first multi-turn conductor wound about a fieldproducing member axis and an input for energizing the first multi-turnconductor to produce an electromagnetic field in the vicinity of theelongated field producing member; b) an elongated field responsivemember fixed with respect to the elongated field producing memberincluding a second multi-turn conductor wound about a field responsivemember axis, said elongated field responsive member oriented in side byside, generally parallel orientation to the elongated field producingmember along a length of the elongated field producing member, andhaving an output for providing an output signal in response to theelectromagnetic field produced by the field producing member; c) a coremember connected to a second of the moveable members for movement withthe second moveable member; said core member mounted for movement withinone of said field producing and field responsive members to alter theresponse of the field responsive member as the moveable members moverelative to each other and thereby change the signal at the output ofthe field responsive member; d) exciter means coupled to the input forenergizing the field producing member; and e) circuit means coupled tothe output from the field responsive member to correlate changes in theoutput signal with relative movement of the moveable members. 12.Movement sensing apparatus for monitoring a relative position andvelocity between two relatively moveable members comprising:a) anelongated field producing member coupled to a first of said moveablemembers and including a first multi-turn conductor wound about a fieldproducing member axis having a first controlled turn density, and aninput for energizing the first multi-turn conductor to produce anelectromagnetic field in the vicinity of the elongated field producingmember; b) an elongated field responsive member fixed with respect tothe elongated field producing member including a second multi-turnconductor wound about a field responsive member axis having a secondcontrolled turn density, said elongated field responsive member orientedin side by side, generally parallel orientation to the elongated fieldproducing member along a length of the elongated field producing member,and having an output for providing an output signal in response to theelectromagnetic field produced by the field producing member; c) acoupling member connected to a second of the moveable members formovement with the second moveable member and positioned relative thefield producing and field responsive members to alter the response ofthe field responsive member as the moveable members move relative toeach other and thereby change the signal at the output of the fieldresponsive member; d) exciter means coupled to the input for energizingthe field producing member; and e) circuit means coupled to the outputfrom the field responsive member to correlate changes in the outputsignal with relative position and velocity of the moveable members,wherein the velocity is obtained by differentiating a position signaloutput.
 13. The apparatus of claim 12 wherein said coupling membercomprises a conductive cylinder with semicircular cross-section.
 14. Theapparatus of claim 12 wherein said coupling member comprises aconductive spring.
 15. Sensing apparatus for monitoring a relativeposition between two relatively moveable members comprising:a) anelongated field producing member coupled to a first of said moveablemembers and including a first multi-turn conductor wound about a fieldproducing member axis and an input for energizing the first multi-turnconductor to produce an electromagnetic field in the vicinity of theelongated field producing member; b) an elongated field responsivemember fixed with respect to the elongated field producing memberincluding a second multi-turn conductor wound about a field responsivemember axis, said elongated field responsive member oriented in side byside, generally parallel orientation to the elongated field producingmember along a length of the elongated field producing member, andhaving an output for providing an output signal in response to theelectromagnetic field produced by the field producing member; c) acoupling member connected to a second of the moveable members formovement with the second moveable member and positioned relative thefield producing and field responsive members to alter the response ofthe field responsive member as the moveable members move relative toeach other and thereby change the signal at the output of the fieldresponsive member; and d) a control module spaced from the elongatedfield producing and field responsive members and electrically coupled tothe field producing and field responsive members by cabling; saidcontrol module including:i) exciter means coupled via said cabling tothe input for energizing the field producing member; and ii) circuitmeans coupled via said cabling to the output from the field responsivemember to correlate changes in the output signal with relative movementof the moveable members.
 16. The apparatus of claim 15 wherein theexciter means and circuit means form part of an application specificintegrated circuit.
 17. The sensing apparatus of claim 15 additionallycomprising an accelerometer for monitoring acceleration of one of thetwo relatively moveable members and wherein the control module comprisesmeans for energizing the accelerometer and monitoring accelerationsignals from the accelerometer.
 18. A control system for monitoringrelative positions between pairs of relatively moveable memberscomprising:a) a plurality of position sensors with each including:i) anelongated field producing member coupled to a first of moveable memberof a given pair and including a first multi-turn conductor wound about afield producing member axis having a first controlled turn density, andan input for energizing the first multi-turn conductor to produce anelectromagnetic field in the vicinity of the elongated field producingmember; ii) an elongated field responsive member fixed with respect tothe elongated field producing member including a second multi-turnconductor wound about a field responsive member axis having a secondcontrolled turn density, said elongated field responsive member orientedin side by side, generally parallel orientation to the elongated fieldproducing member along a length of the elongated field producing member,and having an output for providing an output signal in response to theelectromagnetic field produced by the field producing member; iii) acoupling member connected to a second of the moveable members formovement with the second moveable member and positioned relative thefield producing and field responsive members to alter the response ofthe field responsive member as the moveable members move relative toeach other and thereby change the signal at the output of the fieldresponsive member; and b) control circuitry including exciter meanscoupleable to the input of each position sensor for energizing the fieldproducing member and monitoring means coupleable to the output from thefield responsive member of each position sensor to correlate changes inthe output signal with relative movement of the pairs of moveablemembers.
 19. The control system of claim 18 wherein the controlcircuitry comprises:a) a microprocessor having a control algorithm foractivating the elongated field producing member of the plurality ofposition sensors; b) multiplexor means for coupling electric signals toand from the position sensors; and c) interface means for routingsignals indicative of said relative positions to other circuitry. 20.Position sensing apparatus for monitoring a relative position betweentwo relatively moveable members comprising:a) an elongated fieldproducing member with a first core coupled to a first of said moveablemembers and including a first multi-turn conductor wound about the firstcore situated along a member axis having an input for energizing thefirst multi-turn conductor to produce an electromagnetic field in thevicinity of the elongated field producing member; b) an elongated fieldresponsive member with a second core coupled to a first of said moveablemembers and including a second multi-turn conductor wound about thesecond core situated along a second member axis, said elongated fieldresponsive member oriented in a side by side, generally parallelorientation to the enlongated field producing member, and having anoutput for providing an output signal in response to the electromagneticfield produced by the field producing member; c) a conductive membercoupled to a second moveable member which slides over one or both thefield producing and field responsive members during motion of the secondmoveable member with respect to the first moveable member to alter theresponse of the field responsive member as a result of relative motionbetween the moving members; d) exciter means coupled to the input forenergizing the field producing member; and e) circuit means coupled tothe input from the field responsive member to correlate changes in theoutput signal with relative movement of the moveable members.
 21. Theapparatus of claim 20 wherein said coupling member comprises aconductive compressible bellows.
 22. The apparatus of claim 20 whereinsaid coupling member comprises a conductive spring.
 23. Position sensingapparatus for monitoring a relative position between two relativelymoveable members comprising:a) an elongated field producing memberincluding a core coupled to a first of said moveable members and furtherincluding a first multi-turn conductor wound about said core coupled toa second of said moveable members and an input for energizing the firstmulti-turn conductor to produce an electromagnetic field in the vicinityof the elongated field producing member; b) an elongated fieldresponsive member coupled to the second of said moveable members formovement with respect to the elongated field producing member includinga second multi-turn conductor wound about a field responsive memberaxis, said elongated field responsive member oriented in side by side,generally parallel orientation to the elongated field producing memberalong a length of the elongated field producing member, and having anoutput for providing an output signal in response to the electromagneticfield produced by the field producing member; c) exciter means coupledto the input for energizing the field producing member; and d) circuitmeans coupled to the output from the field responsive member tocorrelate changes in the output signal with relative movement of themoveable members.
 24. The apparatus of claim 23 further including acoupling member for movement with the core and connected to said firstmoveable member that surrounds at least one of said first and secondmulti-turn conductors.
 25. A position sensor, comprising:a) a primarywinding having a first core and a conductor wound around said first coreincluding a multiplicity of turns spaced along at least a portion of alength of said first core; b) a secondary winding having a second coreand a second conductor wound around said second core including amultiplicity of turns space along at least a portion of a length of saidsecond core; c) said secondary winding positioned in a spaced, generallyco-axial transformer coupling relationship with the primary winding withboth said primary and secondary windings attached to a first of tworelatively positioned members; and d) coupling means moveable with asecond of said two relatively positioned members to overlie at least oneof the primary and secondary windings and vary the transformer couplingbetween said windings as the two relatively positioned members move withrespect to each other; e) said primary and secondary windings havingcontrolled turn densities along both their length to provide an outputsignal from the secondary winding that is functionally dependent on therelative position of the two relatively positioned members and saidfirst and second cores comprise magnetic material, the content ofmagnetic material within each core varying along a length of eachwinding.
 26. The sensor of claim 25 wherein the first and second coreshave controlled diameter to adjust the content of magnetic materialalong their length.
 27. The sensor of claim 25 wherein the couplingmeans comprises a ring-shaped permanent magnet and:a) wherein the fluxlinkage between the permanent magnet and the secondary winding increaseslinearly with the position of the magnet along the secondary winding; b)wherein the product of the a.c. flux linkage from the primary winding tothe coupler, and the coupler to the secondary winding, increaseslinearly with the position of the magnet along the seconding winding;and c) said sensor additionally including circuitry for monitoring anoutput from the secondary winding and low pass filtering this output toobtain a velocity dependent signal and high pass filtering followed byamplitude demodulation to obtain a position dependent signal. 28.Position sensing apparatus for monitoring a relative position betweentwo relatively moveable members comprising:a) an elongated fieldproducing member including a core coupled to a first of said moveablemembers and further including a first multi-turn conductor wound aboutand coupled to said core and an input for energizing the firstmulti-turn conductor to produce an electromagnetic field in the vicinityof the elongated field producing member; b) an elongated fieldresponsive member coupled to the second of said moveable members formovement with respect to the elongated field producing member includinga second multi-turn conductor wound about a field responsive memberaxis, said elongated field responsive member oriented in side by side,generally parallel orientation to the elongated field producing memberalong a length of the elongated field producing member, and having anoutput for providing an output signal in response to the electromagneticfield produced by the field producing member; c) a coupling member formovement with the core and coupled with said first moveable member, saidcoupling member surrounding at least one of said first and secondmulti-turn conductors; d) exciter means coupled to the input forenergizing the field producing member; and d) circuit means coupled tothe output from the field responsive member to correlate changes in theoutput signal with relative movement of the moveable members.